Co-option and innovation in neural crest evolution.

The neural crest is one of the most evolutionarily transformative cell lineages in vertebrates. Defined by its migratory capacity and multipotency, it is not a fixed cell type but a transient, shape-shifting stem-like population that redistributes and repurposes diverse cellular programs after germ layer formation. In this opinion piece, we pursue three goals. First, we explore how the neural crest acts as an evolutionary opportunist and a thief, co-opting identities from mesodermal, placodal, and central nervous system lineages to generate novel structures. Second, we distinguish between such co-opted features and true innovations that arise within the permissive neural crest context. Third, we discuss an evolutionary scenario in which the neural crest originated from a photosensory and pigmented cell lineage involved in camouflage and light sensing. During the transition to predation, this ancestral nonessential and, therefore, plastic lineage acquired multipotency and migratory behavior, enabling the emergence of new cell types and contributing to major vertebrate innovations such as the "New Head."